In general, in fillet welding or the like, continuous welding which can obtain high welding strength by continuously welding a series of welding locations, and intermittent welding which intermittently welds a series of welding locations to each other for reducing processing cost and reducing thermal strain, are appropriately selected and used.
As the intermittent welding, parallel welding (or abreast intermittent welding) which intermittently welds one side and the other side of a material in parallel (or abreast) and zigzag welding which intermittently welds both sides in a shape of a zigzag, are known (for example, refer to PTL 1 to PTL 4).